Emission pattern and anti-insect function of indole from tea plants (Camellia sinensis) attacked by tea geometrids

Tea plants (Camellia sinensis) are used to produce beverages that are consumed worldwide. Similar to many other plants, tea plants attacked by herbivores emit herbivore-induced plant volatiles (HIPVs) that enhance defense responses, regulate insect behavior, and send 'warning signals' to neighboring plants. However, the related mechanisms remain relatively unclear. In this study, the anti-insect effects and emission patterns of indole, which is a common HIPV synthesized in tea plants, were investigated. The anti-insect effects of indole may involve the induction of signal transduction pathways and the attraction of natural enemies. An attack by tea geometrids, which are major tea plant pests, resulted in the regular emission of indole. The analysis of plants with simulated insect feeding-induced damages showed that indole emission was higher at noon than at midnight. Additionally, significantly more indole was released by plants maintained under continuous light than by plants kept in darkness. The regular emission of indole may be related to the regular expression of the structural gene CsTSB2. The interaction between CsTSA and CsTSB2 was confirmed, further indicating CsTSB2 likely regulates the regular biosynthesis and emission of indole. The study findings may be relevant to improving environmentally friendly pest control measures in tea plantations.